The publications and other materials used herein to illuminate the background of the invention, and in particular, cases to provide additional details respecting the practice, are incorporated by reference. Many daily goods and special goods resemble dental and medical devices, made from polymers, in the fact that they are prone to fracture due to mechanical conditions of human body or use. In dentistry, it is well documented that removable dentures can fracture after the denture has been worn for some years, (1-3). In orthopedics, bone cements have been proved to be a weak link between e.g. joint implant and bone (4,5). During last few decades, fibre-reinforced composite (FRC) materials instead of unreinforced polymers have been tested as materials more suitable to the dental and medical applications. Attempts have been made to develop a polymer fibre composite material which fullfills the biological requirements and requirements of clinical dentistry and orthopedic surgery for such fibre-reinforced composite material. Recently, an invention of polymer preimpregnated fibre material (prepreg) was introduced for dental and some medical applications (6). Said prepreg made it possible to use fibre composite materials together with multiphase acrylic resins which have relatively high viscosity prior polymerization. The multiphase acrylic polymer are made from prepolymerized powder particles, such as polymethylmethacrylate (PMMA) and monomer liquid, such as methyl methacrylate (MMA) and ethyleneglycol dimethacrylate (EGDMA) (7). Multiphase acrylic resins were used in dental devices and in orthopedic bone cements (7,5). The use of said prepreg resulted in a well impregnated fibre composite with good mechanical properties. Since then, clinical studies have shown that the use of such polymer preimpregnated prepreg eliminates recurrent fractures of acrylic resin removable dentures (8).
Although the above prepreg has resolved the problem to reinforce multiphase acrylic resins of removable dentures with fibres, said prepreg has not resolved certain other problems relating to the use of fibre-reinforced composite materials in dentistry. In many dental applications polymers are made from monomer liquid systems only, instead of powder-liquid mixtures as described earlier. These systems are typically made from dimethacrylate resins, such as BISGMA and triethyleneglycoldimethacrylate (TEGDMA) and polymerized by activation of an initiator by visible light radiation (9). The viscosity of such monomer systems were regulated by changing the ratio of monomers and this resulted in such monomer system which could be used in preimpregnation of fibres with monomers. Such products (Vectris, Vivadent/Ivoclar, Liechtenstein; FibreKor, Jeneric/Pentron, USA) are on the marked. Due to quite difficult handling of dimethacrylate monomer preimpregnated fibres, extensive number of equipment was needed to use these products in dental laboratory. The main problem in this respect with the aforementioned monomer preimpregnation method was that fibres frayed to undesired regions in dentition when the prepregs were placed on teeth. In addition, the processing of the monomer preimpregnated fibres with hand laminating technique sensitize the dental personel to allergy by monomers.
Another great disadvantage of using such monomer preimpregnated fibre systems in dental bridges was that conventional type of tooth preparation was needed. This means that a great amount of dental enamel and dentine was ground in order to get space for the restorative material. This kind of restorative dentistry could be called as "invasive prosthetic dentistry" and one complication of this kind of treatment was hypersensitivity of tooth or necrosis of the pulp tissue. Need for the tooth preparation was minor with so called "resin-bonded-bridges" or "Maryland bridges", which were made from cast metal alloy and luted to tooth with resin cements (10, 11). A disadvantage of this kind of restoration was recurrent debonding of the restoration and relatively high price of the restoration because of complicated laboratory technique (10, 11).
Carbon/graphite and glass fibre-epoxy composites have been developed for use in root canal posts (12, 13). Root canal posts posts were used to restore tooth for an artificial crown. Traditionally, root canal posts were made from individually cast metal alloys or from metal screws. Fibre-epoxy root canal posts might have potential to replace traditionally used materials. However, one shortcoming of the fibre-epoxy composite posts in dental application have been reported. This is inadequate adhesion between resin luting cement and the fibre-epoxy composite post which lead to loosening of the post after some period of time (14). This was due to the highly cross-linked thermosetting polymer structure of the epoxy which did not allow formation of the interpenetrating polymer network (IPN) bonding or radical polymerization bonding (15).
In summary, the problems which relate to the state-of-the-art methods in the field are:
1) Prepregs made from monomer systems were difficult to handle by dentists and dental technicians because preimpregnation monomer did not sufficiently bind the fibres together.
2) Handling of monomer preimpregnated prepregs sensitize dental personel to monomers by skin contact to the prepreg.
3) The treatment with conventional dental bridges required tooth preparation and can be defined as "invasive prosthetic dentistry".
4) By using less invasive prosthodontic techniques, such as resin-bonded-bridges, recurrent debonding of the luting cement from the metal frame of the bridge was a problem.
5) By using currently available fibre-epoxy composite endodontic posts, loosening of the post from the root canal was a problem.
In addition, an unsolved problem with all polymers used in dentistry was the polymerization contraction of the resin (9). This lead to poorly fitting restoration and dentures and caused marginal leakage of restoration.
The use of a semisolid encapsulated fibre roving prepreg was described in the U.S. Pat. No. 4,264,655 (16). In that prepreg, the fibres were preimpregnated with heat-curing thermosetting resin and thereafter covered with a membrane of thermoplastic resin. It was emphasized that the thermoplastic membrane remained distinct part from the thermosetting resin and no bonding was obtained, or desired, between the polymer phases. In addition, thermoplastic membrane was such that it eliminated interstrand adhesion of prepregs.
Another U.S. Patent (U.S. Pat. No. 5,597,631) (17) described a prepreg which had a thermoplastic film coverage. The purpose of the film coverage was to increase the strength of the fibre-reinforced composite made from the prepreg by means of high strength and high modulus of the polymer used in the film coverage. However, this film, although it was bonded to the fibre-rich part of the thermoplastic prepreg, the film was not able to cause interstrand adhesion of the prepregs because the prepreg was thermoplastic in type, which is a desired property for the prepreg used in dentistry.